This invention relates generally to the use of machine vision systems for semiconductor chip bonding/attaching devices. More specifically, the present invention relates to the use of a corner cube retro-reflector as an offset alignment tool that acquires indirect images of optical fibers optic during the alignment process when the same lie outside the view of the imaging system. From such images, coordinate information on position can be obtained and any positional offset from reference position of the fiber optic alignment tool due to deviations caused by thermal change or other nonrandom systemic errors can be taken into account for correct alignment and placement of optical fibers with respect to other optical fibers or fiber optic detectors/devices/elements.
The fabrication of electronic assemblies, such as integrated circuit chips and fiber optic cables, requires alignment inspection of the device at various phases of the fabrication process. Such alignment inspection procedures utilize vision systems or image processing systems (systems that capture images, digitize them and use a computer to perform image analysis) to align devices and guide the fabrication machine for correct placement and/or alignment of components.
In conventional systems, post attach inspection is used to determine if changes in fabrication machine position are necessary to effect proper placement and/or alignment. As such, these conventional systems can only compensate for misalignment after such improper alignment is made, thereby negatively effecting yield and throughput. These conventional systems have additional drawbacks in that they are unable to easily compensate for variations in the system due to thermal changes, for example, requiring periodic checking of completed devices further impacting device yield and negatively impacting manufacturing time.
In conventional systems the vision system (shown in FIG. 11) consists of two image devices, a first image device 1104 placed below the optical plane 1112 and views objects upward and a second image device 1102 placed above the optical plane and views objects downward. These conventional systems have drawbacks, in that in addition to requiring more than one image device, they are unable to easily compensate for variations in the system due to thermal changes, for example.
In view of the shortcomings of the prior art, it is an object of the present invention to provide a system and method for aligning optical fibers using a vision system that takes into account variations due to temperature changes and other nonrandom systemic effects.
The present invention is a vision system for use in aligning optical fibers. The system comprises an alignment tool having a plurality of internal reflection surfaces, the alignment tool located below a vision plane of the first optical fiber; and an optical detector to receive an indirect image of a bottom surface of the first optical fiber through the alignment tool.
According to another aspect of the invention, the vertex of the alignment tool is located at a position about midway between the optical axis of the optical detector and the optical axis of the first optical fiber.
According to a further aspect of the invention, the alignment tool comprises a cornercube offset tool.
According to still another aspect of the invention, the focal plane of the vision system is positioned at or above the alignment tool.
According to yet another aspect of the present invention, the system includes a lens positioned between the alignment tool and i) the optical detector and ii) the first optical fiber.
According to still another aspect of the present invention, the system includes a first lens positioned between the optical detector and the alignment tool and a second lens positioned between the first optical fiber and the alignment tool.
According to a further aspect of the present invention, the first lens and the second lens are located at or below the image plane.
According to yet a further aspect of the present invention, the reflecting surfaces are three mutually perpendicular faces.
According to yet another aspect of the present invention, the angle between each of the internal reflective surfaces and the top surface of the cornercube offset tool is about 45xc2x0.
According to still another aspect of the invention, the optical detector is a CCD camera.
According to yet another aspect of the invention, the optical detector is a CMOS imager.
According to yet a further aspect of the invention, the optical detector is a position sensitive detector.
According to an exemplary method of the present invention, a cornercube offset tool is positioned below a vision plane of the first optical fiber; a lens is positioned between i) the first optical fiber and the cornercube offset tool and ii) between the optical imager and the cornercube offset tool; and the first optical fiber is viewed indirectly through the cornercube offset tool and the lens.
These and other aspects of the invention are set forth below with reference to the drawings and the description of exemplary embodiments of the invention.